Restart browser once in a while during unit testing

The unit testing on mac is unreliable, making the last tests to hang.
This seems to be related to the upstream bug: crbug.com/741689

For now, this patch restarts the browser in the middle of unit testing.
This should be reverted once the upstream is fixed.

References #100.

test/test.js

@@ -835,6 +835,14 @@ describe('Puppeteer', function() {
       expect(keyboard.modifiers().Alt).toBe(false);
     }));
   });
+
+  // FIXME: remove this when crbug.com/741689 is fixed.
+  it('RESTART BROWSER crbug.com/741689', SX(async function() {
+    page.close();
+    browser = new Browser({headless, args: ['--no-sandbox']});
+    page = await browser.newPage();
+  }));
+
   describe('Page.setUserAgent', function() {
     it('should work', SX(async function() {
       expect(page.userAgent()).toContain('Mozilla');